While mobile responsive and mobile adaptive websites are beneficial, they are also quite different than one another. Both change their dimensions based on the browser or device, however, mobile adaptive sites only adapt at certain points. Rather than fluidly altering in size, the browser must be a particular width for content to be set in place. Basically, an adaptive website has multiple layouts based on the size of the browser.
Take a look at Steve Madden’s adaptive website below at normal width.
Now, look below again. The browser is a tad narrower but the tabs disappear and the logo remains the same.
Everyone should have a mobile-friendly site but not everyone needs an adaptive or responsive website. An adaptive website is cheaper and loads faster especially since images are scaled down and not resized. If your website is complex (ie: e-commerce) it may be best to create a responsive website.